A wireless repeating technology separating transmitting/receiving signals in an antenna can be divided into a unidirectional repeating system and a bi-directional repeating system. A reception direction and a transmission direction are different from each other in the unidirectional repeating system, but they are the same in bi-directional repeating system.
Herein, a conventional unidirectional repeating system is a technology which can acquire high isolation by setting up antennas of high directivity in opposite directions with space between them. The technology is generally applied to a large repeater system such as a TV and a radio.
However, since the conventional technology requires isolation space between a transmitting antenna and a receiving antenna, it has a problem that a large space is required for setting up the antennas.
There is other conventional technology for generating transmission and reception signals whose polarization is vertical to each other by vertically setting up a feeder in a patch antenna and maintaining isolation between two terminals, although the technology is not practically applied to a system. The technology is revealed in an article by Karode, IEE National Conference on Antennas and Propagation, April 1999, pp. 49-52.
Also, Hao has realized an isolation technology by differently generating polarization of a patch antenna which applies a structure of Photo Band Gap (PBG) in an article, IEE 11th International Conference on Antenna Propagation, April 2001, pp. 86-89.
However, since isolation in a co-frequency for transmitting/receiving signals are very low as suggested in the above-result, there is a problem that the patch antenna is not proper to co-channel bi-directional communication in diverse mobile communication, local area network, broadcasting repeater and satellite communication fields which require high isolation in a co-frequency.
Also, the conventional technologies suggested by Karodo and Hao obtain isolation of less than 60 dB although transmitting/receiving frequency bands or polarizations are different from each other. Accordingly, it has a problem that isolation is not high sufficiently.
Therefore, the above-described conventional transmitting/receiving isolation technology cannot be used for an isolation antenna for a repeater requiring ultra isolation of more than 100 dB.